154650-88-1

59944-76-2

Methyl thieno[2,3-b]pyridine-2-carboxylate (C101, 0.700 g, 3.63 mmol) was used as a raw material and dissolved in a solvent mixture of methanol (15 mL) and water (3 mL). At room temperature, 2N sodium hydroxide solution (1.82 mL, 3.63 mmol) was added dropwise and the reaction mixture was stirred for 24 hours. Upon completion of the reaction, the mixture was concentrated under vacuum to remove most of the solvent. Subsequently, water (40 mL) was added to dissolve the residue. The resulting solution was acidified to pH 4 with concentrated hydrochloric acid, at which point thieno[2,3-b]pyridine-2-carboxylic acid (C102) precipitated as a white precipitate. The precipitate was collected by filtration to give the target product in 85% yield. The product was analyzed by mass spectrometry (EI) and showed a molecular ion peak m/z of 179 (M+), which is consistent with the theoretical value of the molecular formula C8H5NO2S.